Global warming-related sea level rise constitutes a major threat to the nation’s capital, with the potential to inundate national monuments, museums, military bases, and parts of the Metro Rail system during the next several decades and beyond, according to a recent study published in the journal “Risk Analysis.” The study helps localize a problem that is more typically discussed at the global level, and makes clear that public officials must make decisions in the near-term in order to minimize future losses.

Considering the city’s history, it should come as no surprise to learn that Washington, D.C. is vulnerable to sea level rise. The National Mall and Foggy Bottom were originally marshland, and the area between the Anacostia River and I-295 used to be open water. What is rather disturbing and less well known, though, is just how vulnerable D.C. is to even minor amounts of sea level rise, which according to some studies is virtually guaranteed as the amounts of greenhouse gases in the atmosphere continue to climb, temperatures rise, and mountain glaciers and ice caps melt.

The study, led by Bilal Ayyub of the University of Maryland, found that even if sea level rise turns out to be at the very low end of projections, it would still cause significant damage in Washington. For example, if the local sea level were to rise by just 0.1 meter, or about 4 inches, by 2043, nearly 68,000 people would be affected, and property damage would total upwards of $2 billion - without including damage to military bases and government property.

The study points out the vulnerability of the military installations the line the Potomac River, particularly Bolling Air Force Base, which would lose 23 buildings to inundation by 2043 if sea level rise proceeds at its recent rate, and many more if it speeds up.

The linear model projects sea level rise of 0.12 meter (about 4 inches) by 2050, 0.27 meters (about 11 inches) by 2100, and 0.42 meters (about 17 inches) by 2150. By comparison, other studies have projected around one meter, or 3.3 feet, of global sea level rise by 2100, which could prove disastrous for D.C. and many other coastal locations.

Even without massive amounts of sea level rise, the city already experiences coastal flooding from astronomical high tides and severe weather events. The most recent storm to cause major flooding was Tropical Storm Isabel in 2003. Last April, astronomical high tides combined with unusually heavy rain to cause flooding along the Georgetown waterfront and in Alexandria.

Most of the sea level rise that has taken place so far has mainly been caused by the thermal expansion of seawater as the oceans have warmed, but the majority of projected sea level rise will come from mountain glaciers and the ice sheets of Greenland and Antarctica. The ice sheets are already melting faster than recent projections had anticipated, and how they will respond to additional global warming is one of the biggest wild cards in climate science today.

As the study states (using the abbreviation “SLR” for “sea level rise”):

A seal level rise is an inevitable future for Washington, DC that would impact the city even with a relatively small rise. Current predictions range from a modest SLR of 0.2 meters to a more dramatic rise of 2.15 meters in the next 100 years. The linear model described in this article underpredicts the SLR compared to other models and places it at 0.42 meters by 2150.

The study makes clear that even modest amounts of sea level rise would have negative impacts on the city:

At 0.1 m SLR, the impact seems deceptively small. The city, however, would have to act. The city has the option to accommodate to the increasing levels by insulating buildings, the metro, and allowing some areas to flood. As Washington, DC is an important political and cultural center of the United States, this option will inevitably cause damage, and leave the city vulnerable to further rises in SLR. Protecting the city by building flood barriers might be a more practical solution. At the current predictions, the barriers do not have to be especially high to protect the city. As sea levels increase, they would have to be increased in height and reinforced. City planners should also consider SLR in defining or changing land use.

As the Post reported in November of 2010, the federal government has already begun improving Washington’s flood defenses, but the study notes that current plans would have to be enhanced in order to offer a more viable longer term sea level rise protection strategy.